Recently the installation of monitoring cameras in stores, downtowns, apartment buildings, etc., and the installation of drive recorders in vehicles for business use and the like have become popular, and cases of using moving images as evidence have been increasing. It has also become a common practice to record communications between customers and telephone operators and to store them as evidence in order to cope with troubles in business agreements and in support businesses conducted over the telephone.
Currently, when moving images and audio recordings are used as evidence, video tapes and image/audio files are provided without being processed. However, if the digitization of image/audio storage progresses, it will become easy to alter or edit these media, and when they are used as evidence, third party verification such as a signatures and a time stamp will become necessary. Indeed, services and products for recording the audio of a telephone operator with a time stamp are already being sold, and it is anticipated that such a technical need will increase.
Furthermore, providing a digital signature is an important technique for assuring the security of electronic data and is applied to agreements, applications, and the like in order to authenticate the producer of the data or to prove that the data has not been not altered. Electronic data to which a digital signature is attached is designed in such a way that the alteration of even one bit can be detected, and is useful in protecting electronic data from unauthorized persons.
However, with the increase in the use of monitoring cameras and the like, the protection of privacy in the use of pictures and video recordings has become a problem; this issue has been discussed in the Ministry of General Affairs and the like. The use of individual private information is also severely restricted by the enforcement of the Individual Privacy Protection Law and the like, and upon request its disclosure, partial deletion, and the like is necessary. In addition, when a long recording of video/audio data is made the amount of data becomes enormous, and when it is presented as evidence, it is necessary to extract the necessary portions.
Thus, since no processing is allowed when a digital signature is applied, it can become an obstacle from the viewpoint of the valid use of electronic data, such as with the partial deletion of data or the extraction of a necessary portion of private information.
In order to cope with two such problems, the need for evidence of electronic data and the need for privacy protection, research into the assurance of the partial originality (completeness) of a portion of an electronic document and a sanitizable signature technology for keeping it secret has been promoted.
More particularly, Patent document 1 below discloses a sanitizable signature technology for an electronic document, for solving the problem of a signature attached to certain document not being able to be verified because a portion of the document is being kept secret (hereinafter abbreviated and explained as PIAT).
By applying this PIAT, a signature can be verified in a state where sanitizing is applied to an electronic document with the signature and it can be proven to a third party that no portion of an original has been altered or added to except for the sanitized portion.
A technology for applying the technology of Patent document 1 to moving image/audio data and realizing the assurance of originality of these pieces of data and the extraction of privacy protectable data from a signature-target is also disclosed in Patent document 2 below.
According to these technologies, even if a portion of moving image/audio data is cut out, it can be proven to a third party that it is a portion of the original and has not been altered.
Furthermore, a media format called Motion-JPEG exists as compressed moving image data. The Motion-JPEG is a compressing/recording method for generating moving image data by using the JPEG (Joint Photographic Experts Group) format, which is a compressing method of a still image; it disposes a compressed JPEG still image in each frame and reproduces it like animation.
Since compression is applied to each frame, the reproduction ratio of Motion-JPEG is high. High-quality recording is possible, an arbitrary point can be quickly accessed, and even a single cut can be made. Recently the camera function of cellular phones compatible with the taking of a still or moving image and the like have adopted Motion-JPEG.
In this Motion-JPEG there are two formats (container formats), AVI (Audio Video Interleave) developed by the Microsoft Corporation and MOV developed by the Apple Corporation.
In particular, the AVI format may be divided into a header (property) and a body (content). The header stores information for reproducing a moving image and audio, such as the number of JPEG still images stored in the body (number of frames), the size of an image, a frame rate, and the like. The body sequentially stores respective pieces of real data of the moving image/audio.    Patent document 1: International Publication Pamphlet No. WO 2006/008847    Patent document 2: Japanese Laid-open Patent Publication No. 2008-178048